From: Cao jin <caoj.fnst@cn.fujitsu.com>
To: <linux-kernel@vger.kernel.org>
Cc: peterz@infradead.org, "Izumi, Taku/泉 拓" <izumi.taku@jp.fujitsu.com>
Subject: about definition of iowait
Date: Tue, 7 Jun 2016 19:24:46 +0800 [thread overview]
Message-ID: <5756AEFE.60300@cn.fujitsu.com> (raw)
Hi,
I noticed some problems about iowait entry of /proc/stat: it seems not
accurate, and sometimes will decrease in SMP.
For UP, we have a simple definition about iowait, which is:
The time that the processor is idle, during which there is a task
waiting for I/O.
This definition seems don't fit well when step into SMP era, so I think
maybe it can be extended like:
For a given CPU, the I/O wait time is the time during which that CPU was
idle, and there is at least one outstanding disk I/O operation requested
by a task scheduled on that CPU.
But tasks can migrate among cpus, so this definition maybe not accurate.
I also saw some suggestions that it should be a global value, not per
cpu, but don`t see clear definition, so anyone have suggestions about
it? (personally guessing, maybe: there is task waiting for outstanding
I/O while all cpus are idle? But I don't think it is good...)
--
Yours Sincerely,
Cao jin
next reply other threads:[~2016-06-07 11:19 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-07 11:24 Cao jin [this message]
2016-06-07 12:01 ` about definition of iowait Peter Zijlstra
2016-06-08 7:14 ` Cao jin
2016-06-27 6:06 ` Cao jin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=5756AEFE.60300@cn.fujitsu.com \
--to=caoj.fnst@cn.fujitsu.com \
--cc=izumi.taku@jp.fujitsu.com \
--cc=linux-kernel@vger.kernel.org \
--cc=peterz@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).